Each year, the secondary metals industry recovers about 55-60.times.10.sup.6 tons of scrap that is used in the production of finished steel products. The single largest source of this scrap is the obsolete automobile. The shredder industry recovers about 10-12.times.10.sup.6 tons/yr. of ferrous scrap, most of which is from shredded automobiles. However, for each ton of steel recovered, about 500 lbs. of shredder fluff is produced. Shredder fluff consists of the nonmetallic content of the automobile and other materials (and their constituents), such as air conditioners, refrigerators, dryers, and dishwashers, the latter products are commonly called white goods. At present, shredder fluff is disposed of in landfills; however, the rapidly escalating cost of landfilling, as well as concerns about the fate of this waste in the environment, poses a significant liability to the industry.
Shredder fluff is a very heterogeneous waste material; not only does its composition vary from site to site, but it changes daily even at the same site. Shredder fluff contains plastics [thermoplastics, thermosets, and polyurethane foam (PUF)], rubber, wood, paper, fabrics, glass, sand, dirt, ferrous and nonferrous metal pieces, tar and any other materials that may remain in a vehicle when it is scrapped. Overall, shredder fluff consists of about 50% combustible material and 50% noncombustible (inert) material. The plastics content of shredder fluff is typically about 15-30% by weight. This proportion is expected to increase over the next decade because the use of automotive plastics has increased significantly over the past 10-15 yr. The shredder fluff may also contain brake fluid, gasoline, engine oil, windshield washing fluids, antifreeze (ethylene glycol), FREON.TM. refrigerants, and in some cases polychlorinated biphenyls (PCBs). PCB contamination can result from the shredding of old white goods that may have intact capacitors. In addition, shredder fluff may contain heavy metals, such as lead, mercury, and cadmium. Shredder fluff also contains varying amounts of moisture, depending on the type of shredding operation (i.e., wet or dry) and if it is exposed to rain while in inventory. An approximate composition of shredder fluff is as follows:
Plastics 15-30% Paper, wood, oils and tar 15-25% Inert material 25-75% Moisture 2-35%
The composition of the plastics portion of a 1981 model U.S. passenger car was reported (McClellan, T. R., 1983 in Modern Plastics, pp. 50-52, Feb.) to include the following:
 Polyurethane foam (PUF) 23% Reinforced plastics (RP), bulk molding 22% compound (BMC), and sheet molding compound (SMC) Polypropylene (PP) 19% Polyvinyl chloride (PVC) 15% Acrylonitrile butadiene styrene (ABS) 7% Nylons 4% Other 10%
Thermoplastics (such as PP, ABS, and PVC) appear to account for a significant share of the plastics anticipated to be contained in shredder fluff, and the economic recovery of these materials is an aspect of this invention.
The density and shape of shredder fluff is heterogeneous. For example, the PUF, with absorbed moisture and oils, might represent about 10% of the shredder fluff mass but could represent over 50% of its volume. On the other hand, fines (&lt;1/4 in.) might represent abut 25% of the mass and only 5% of the volume. The volume ratios of the large and small PUF pieces could be as high as 250:1. The physical variability of shredder fluff is problematic for recyclers and is obviously of significant importance in the development of efficient reclamation technology.
Although a number of alternatives for the disposal, treatment, and recycling of shredder fluff are the subject of ongoing research and development, most are not cost-effective, and none focus on the recovery of thermoplastics from shredder fluff for their reuse as thermoplastics. Even the conversion of shredder fluff to fuels and chemicals is a loss in the potential value of plastics, which are derived from fuels and chemicals in the first place. The concept of recovering plastics from shredder fluff for reuse as plastics is appealing for the following reasons: (1) the plastics content of shredder fluff is expected to increase, (2) the market for plastics use in automobiles is growing, and (3) the plastics recycling industry, although still in its infancy, is growing, and we believe that it will continue to grow.
Thermoset plastics (which cannot be reused as plastics except as fillers in composites) are not soluble in organic solvents, although many thermoplastics are. On the basis of the expected plastics content of shredder fluff presented, we expect that more than 60% of the total thermoplastics content of shredder fluff might be recoverable through the dissolution of the plastics in solvents. Conceptually, because of differences in the solubilities of certain plastics and their differences in susceptibility to specific solvents, the intent of the envisioned basic process concept was to develop a process for extracting specific individual plastics or groups of compatible plastics from shredder fluff using solvents.